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Overcoming chemical equilibrium limitations using a thermodynamically reversible chemical reactor

Abstract

All real processes, be they chemical, mechanical or electrical, are thermodynamically irreversible and therefore suffer from thermodynamic losses. Here, we report the design and operation of a chemical reactor capable of approaching thermodynamically reversible operation. The reactor was employed for hydrogen production via the water–gas shift reaction, an important route to ‘green’ hydrogen. The reactor avoids mixing reactant gases by transferring oxygen from the (oxidizing) water stream to the (reducing) carbon monoxide stream via a solid-state oxygen reservoir consisting of a perovskite phase (La0.6Sr0.4FeO3-δ). This reservoir is able to remain close to equilibrium with the reacting gas streams because of its variable degree of non-stoichiometry and thus develops a ‘chemical memory’ that we employ to approach reversibility. We demonstrate this memory using operando, spatially resolved, real-time, high-resolution X-ray powder diffraction on a working reactor. The design leads to a reactor unconstrained by overall chemical equilibrium limitations, which can produce essentially pure hydrogen and carbon dioxide as separate product streams.

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Fig. 1: Thermodynamic reversibility in a WGS reactor.
Fig. 2: Conversion, reactor performance measure (K*) and outlet mole fractions (real and modelled) versus cycle number show that equilibrium limitations have been overcome.
Fig. 3: Representative shifts in 2θ peak positions and local oxygen content of the LSF versus reactor position showing changes in lattice parameter and oxygen content are a function of axial position.

Data availability

Data supporting this publication are openly available under an ‘Open Data Commons Open Database License’. The data, with additional metadata, are available at https://doi.org/10.17634/080913-1.

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Acknowledgements

C.R.T. and C.d.L. thank EPSRC for funding via a doctoral training award. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC grant agreement no. 320725 and from the EPSRC via grants EP/G012865/1, EP/J016454/1, EP/K029649/1, EP/P007767/1 and EP/P024807/1. The authors thank A. Fitch, C. Giacobbe, M. Coduri and O. Grimaldi at ESRF for help with XRD and T. Ingham, IGI Systems, for constructing the custom flow system and furnace. The authors also thank A. Coelho for developments in Topas to enable analysis of the multiple X-ray data sets produced, and B. Ladewig for help in producing the video.

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I.S.M. conceived the overall idea, secured funding and managed the work. I.S.M. and J.S.O.E. wrote the main text. I.S.M., B.R., W.H., C.d.L. and J.S.O.E. were responsible for the data analysis, modelling and interpretation. B.R., C.De., C.d.L., C.Du., F.R.G.-G., C.-M.M., E.I.P. and C.R.T. performed the experiments.

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Correspondence to Ian S. Metcalfe.

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Supplementary information

Supplementary information

Supplementary Methods, Supplementary Analysis, Supplementary Results, Supplementary Modelling, Supplementary Figs. 1–10, Supplementary Tables 1–6

Supplementary Video 1

A video that shows the principle of operation of the chemical memory reactor

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Metcalfe, I.S., Ray, B., Dejoie, C. et al. Overcoming chemical equilibrium limitations using a thermodynamically reversible chemical reactor. Nat. Chem. 11, 638–643 (2019). https://doi.org/10.1038/s41557-019-0273-2

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